The Children's Cancer Study Group is a multidisciplinary cooperative group of investigators from 26 institutions in the United States and Canada collaborating in the development, implementation and completion of prospective, randomized clinical trials in pediatric hematologic malignancies and solid tumors, including acute lymphoblastic leukemia (ALL), acute nonlymphoblastic leukemia (ANLL), brain tumors, lymphomas (non-Hodgkin's and Hodgkin's), Wilms' tumor, neuroblastoma, rhabdomyosarcoma, bone tumors, hepatoblastoma, "histiocytosis X", and retinoblastoma. Natural history, biologic characterization of cancer (pathology, immunology, biochemistry), prognostic factors, late effects and supportive care aspects are also stressed in these studies involving pediatric oncohematologists, surgeons, pathologists, diagnostic and therapeutic radiologists, neurologists, psychiatrists, psychologists, cell biologists, immunologists, and infectious disease specialists. New agent Phase II trials for patients failing initial therapy and new modalities of therapy including bone marrow transplantation, are additional major thrusts of the cooperative group. MSKCC - NYH-CMC (and its affiliates) has been a major contributor to the efforts of the Group. This research proposal outlines the center's participation in present and future CCSG endeavors at the executive level as well as in the development of new pilot studies for eventual groupwide participation.